Snubber mechanism



A ril 21, 1970 M. L. KLUCZYNSKI ET AL 3,507,190

SNUBBER MECHANISM Filed April 16. 1968 INVENTORS MA ZUCZV/VSK/ C. 5A AZEY ATTO N EY United States Patent O 3,507,190 SNUBBER MECHANISM Mathew L. Kluczynski, Lakeview Terrace, and Charles M. Braley, Sylmar, Califl, assignors to Borg-Warner Corporation, Chicago, 11]., a corporation of Delaware Filed Apr. 16, 1968, Ser. No. 721,706 Int. Cl. Fb 15/22 US. Cl. 91395 1 Claim ABSTRACT OF THE DISCLOSURE A piston type actuator having means for deceleration of the piston upon reaching the limit of its stroke. The deceleration means includes a spring biased snubber slidable upon the piston shaft and defining therewith a variable area orifice. The snubber, at a predetermined position of piston movement traps a quantity of working fluid placing the orifice intermediate the trapped fluid and the fluid discharge. Further movement of the piston causes the fluid to flow through the orifice to decelerate the piston and effect movement of the snubber with respect to the shaft to vary the orifice size.

BACKGROUND OF THE INVENTION This invention relates to a piston type actuator. More particularly it relates to piston type actuators including a mechanism for controlling piston deceleration.

Mechanical actuators, commonly utilized to provide physical movement in response to application of hydraulic pressure generally include a movable piston connected to an operating shaft. The operating shaft moves upon application of hydraulic pressure to the piston to position a mechanical mechanism coupled to the operating shaft.

One serious problem encountered in actuator design is that of deceleration of the piston as it nears the end of its stroke. This deceleration is necessary to prevent damage to the actuator components occasioned by impact of the piston with the cylinder end wall. Also, gradual deceleration reduces operating shaft velocity and also the rate of change of position of the mechanical mechanism. Such a feature is desirable in many applications such as in the use of actuators to position the control surfaces of aircraft. Many forms of deceleration mechanisms have been used. One arrangement traps a portion of the hydraulic fluid being discharged from the cylinder by virtue of movement of the piston toward one end Wall and passes it through a restricted orifice to convert the kinetic energy to heat.

The structural configuration necessary to accomplish deceleration in this manner has proven to be quite complex. Such arrangements have required separate by-pass passages, non-metallic seals in critical areas which are subjected to substantial pressures, and restricting orifices disposed in the discharge line. Normally, the restricting orifices are fixed in the sense that orifice size does not vary as pressure decreases. Thus the deceleration rate is variable, very high at the initiation of deceleration and low as the piston reaches its limit of travel.

Accordingly, it is the principal object of the present invention to provide an improved actuator having a decelerating mechanism which eliminates the need for separate by-pass passages and non-metallic seals and provides for smooth deceleration of the piston.

quantity of trapped fluid to decelerate the piston as it reaches the limit of its stroke.

3,507,190 Patented Apr. 21, 1970 The actuator includes a cylinder defining a chamber within which is disposed a movable piston connected to an operating shaft. A spring biased snubber is slidably disposed upon the shaft and resiliently urged into a position spaced from the piston intermediate the piston and an end wall of the chamber. The snubber and shaft cooperate to define a variable area orifice. Movement of the piston toward the chamber end wall causes the snubber to contact the wall and trap a portion of the working fluid. Further movement causes the fluid to pass through the orifice to effect piston deceleration. As deceleration takes place the snubber slides with respect to the shaft to reduce the orifice area.

DESCRIPTION OF THE DRAWINGS the apparatus in a different position;

FIGURE 3 is a fragmentary view of an enlarged scale of a portion of the apparatus of FIGURE 1.

DETAILED DESCRIPTION Referring now to the drawings, there is illustrated a piston type actuator generally designated 10 constructed in accordance with the principles of the present invention.

The actuator 10 includes a cylinder 12, a reciprocable piston 14, operating shaft 16 and a deceleration mechanism 18.

The cylinder 12 defines an operating chamber 20' having a cylindrical wall 22 and transverse end Walls 24 (one of which is shown). The opposite wall, not shown, may be considered to be similarly constructed. The end walls 24 include a cylindrical opening 26 defining support surfaces 27. An annular recess 28 is provided adjacent the cylindrical opening 26 defining a circular seat 30. A fluid passage 32 is provided in the cylinder 12 which communicates between the recess 28 and a source of fluid pressure (not shown). A similar fluid passage (not shown) is provided at the opposite end wall of the cylindrical wall 22. These passages provide for entry and discharge of fluid into and out of the operating chamber 20.

The reciprocable piston 14 is disposed within the operating chamber 20 in sliding contact With the cylindrical wall 22.

The piston 14 divides the chamber 20 into two portions, each one of which is associated with one of the end walls 24. As the piston moves, one of the chamber portions expands in volume and the other contracts depending on the direction of piston movement. An annular seal 34 is connected to the piston 14 and includes a surface 36 in sliding contact with the cylindrical wall 22 to prevent leakage across the piston.

The piston 14 is adapted for movement between the limits defined by the .end walls 24 in response to application of fluid pressure to one side of the piston or the other. Pressurization of the chamber on one side of the piston through one of the fluid passages 32 causes movement of the piston toward the opposite end wall. This causes fluid trapped in the contracting portion of the chamber to be purged from the chamber through the fluid passage. When the direction of the piston movement is reversed the fluid direction is also reversed and fluid is discharged from the opposite passage.

The operating shaft 16 is generally cylindrical and is slidably supported by the support surfaces 27. The fit between the operating shaft 16 and the support surfaces 27 is extremely close and is essentially fluid tight. If desired a seal (not shown), such as an O-ring seal, may be provided between the shaft 16 and the support surfaces 27.

The operating shaft is secured to the piston for reciprocal movement therewith. The operating shaft is, in turn, connected to some mechanical mechanism (not shown) to eifect positioning of certain movable elements in response to pressurization of one or the other of the chamber portions.

The shaft 16 includes a peripheral groove 37 spaced from the piston 14. A removable retaining ring 38 is disposed in the groove which has an outer diameter slightly larger than the shaft 16.

Intermediate the groove and piston there is provided a flat ramp 39 tapering slightly radially inwardly in a direction toward the groove 37. The ramp defines a relieved portion extending between the groove 37 and the piston 14. Since the ramp is formed at a slight angle to the shaft centerline the planar surface has a varying width and depth'below the outer diameter of the shaft which is a maximum adjacent the groove and a minimum adjacent the piston (see FIGURE 1).

The deceleration mechanism 18 includes an annular snubber or poppet 40 slidably disposed in surrounding relation to the shaft 16 intermediate the retaining ring 38 and the piston 14. The snubber is made of metal or the like and includes an annular body portion 41 and an integrally formed annular head portion 42.

The snubber or poppet hody portion 41 includes an inner cylindrical surface 44 sized to fit slidably upon the outer surface of the shaft with only a minimal clearance between the relatively movable surfaces. The axial width of the inner cylindrical surface 44 is less than the distance between the retaining ring 38 and the piston 14 and the snubber is therefore free to slide upon the shaft within these limits. The inner cylindrical surface overlies the flat ramp 39 formed on the shaft and since the ramp 39 is depressed radially inwardly from the cylindrical outer diameter of the shaft, these two elements combine to form an orifice 46, (best seen in FIGURE 3). Since the ramp is tapered slightly radially outwardly toward the piston, a variable orifice is formed having a maximum area when the snubber is adjacent the ring 38 and a minimum area when the snubber is adjacent the piston 14.

The snubber body portion further includes an outer, generally conical, surface 48 overlying the inner cylindrical surface 44. Fluid pressure upon this surface imparts a radial force component to the body portion insuring a generally fluid tight seal between the shaft inner surface and the snubber except in the area of the orifice 48.

The snubber enlarged head portion 42 includes a conical sealing surface 50 adapted for sealing engagement with the seat 30 of the cylinder 12. A generally annular reaction surface 52 is also provided upon the head portion 42.

The head portion 42 includesan inner cylindrical surface 54 having a diameter larger than the outer diameter of the retaining ring 38 and defining with the shaft 16 and annular passage 56.

A step 58 formed at the transition between the inner cylindrical surface 44 of the body portion 41 and the inner cylindrical surface of the head portion 42 provides a stop for engagement with the ring 38 to limit axial movement of the snubber.

A compression coil spring 60 is disposed intermediate the piston 14 and the reaction surface 52 to urge the snubber to its extended position with the step 58 in contact with the retaining ring 38.

The snubber 40 cooperates with the end wall 24 of the chamber 20 and the shaft 16 and piston 14 to decelerate the piston as it approaches the wall.

When the elements are disposed as shown in FIGURE 1, no deceleration forces are imparted to the piston by the mechanism 18. Movement of the piston 14 toward the 'wall 24 causes fluid in the contracting portion of the chamber to pass out of the chamber through the recess 4 v i 28 and fluid passage 32 until the elements assume the position shown in FIGUR'E 2. At this point the conical sealing surface comes into contact with the seat 30 and traps a quantity of fluid in the chamber 20 between the snubber 4t) and the piston. Continued movement of the piston 14 toward the wall 24 causes compression of the coil spring which normally urges the step 58 into contact with the sealing ring 38. This action causes trapped fluid to pass between the flat ramp 39 and the inner cylindrical surface 44 of the snubber body portion into the annular passage 56 defined by the snubber head portion 42 and the operating shaft 16.'The fluid is then free to pass into the recess 28 and discharge passage 32. Passage of the fluid through the orifice 46 converts the kinetic energy of the piston to heat and accomplishes deceleration of the piston. Once the snubber contacts the seat 30 it is precluded from further axial movement. The piston and operating shaft however continue to move continually changing the relationship between the flat ramp 39 and reducing the etfective orifice size. This is true since the flat ramp 39 is tapered toward the outer cylindrical surface of the shaft in a direction toward the piston. This relationship provides for smooth deceleration throughout the entire stroke of the snubber.

As stated, the outer surface of the body portion is slightly conical. Pressure of the trapped fluid acts upon this surface insuring an essentially fluid tight seal between the shaft and snubber. This prevents any undesirable leakage in areas other than at the flat ramp39.

When pressurized fluid is directed to the contracted portion of the chamber through the passage 32 it enters the recess 28 and exerts an axial force upon the snubber 40 and piston 14. This causes the piston to move away from the wall 24 toward the opposite end of the chamber 20. The piston 14 and shaft 16 move with respect to the snubber 40 until the step 58 engages the retaining ring 38 and thereafter the snubber is moved with the shaft. The spring then retains the snubber in this position for repetition of the deceleration cycle.

While only one deceleration mechanism is shown it must be appreciated that deceleration of movement in either direction could be important and that two deceleration mechanisms could be provided on either side of the piston.

As can be seen, an improved actuator has been provided which includes an improved deceleration mechanism which eliminates the need for separate by-p-ass passages in the cylinder body and complicated resilient seals and further provides smooth deceleration of the piston.

What is claimed is:

1. A piston type actuator comprising a cylinder defining an elongated operating chamber including at least one end wall defining an opening, means defining a recess surrounding said opening forming a seat surface, said cylinder defining a fluid passage communicating with said recess and adapted to admit and discharge fluid from said chamber, a movable operating piston in said chamher, a cylindrical operating shaft integral with said piston and extending from said chamber through said opening, said shaft including .an axially extending flat ramp adjacent said. piston, at least a portion of which is disposed radially inwardly of the shaft outer cylindrical surface, and a deceleration mechanism including an annular snubber surrounding said shaft, said snubber including a body portion having an inner cylindrical surface slidably engaging said shaft in overlying relation to said ramp to define an orifice therebetween and a head portion adapted for engagement with said seat formed on said end wall,.

said orifice including a plurality of axially extending tapered slots formed in said shaft defining a variable orifice with movement of said head relative to said shaft, said mechanism further including means resiliently urging said snubber into a first position in spaced relation to said piston in a direction toward said end wall and allowing movement of said snubber with respect to said shaft toward said piston, movement of said piston toward said end wall causing said head portion to engage said seat to trap a quantity of fluid, continued movement of said piston urging the trapped fluid to said passage in said cylinder through said orifice, means including a 5 groove and ring positioned on said shaft removably connecting said head to said shaft.

6 References Cited UNITED STATES PATENTS 2,412,975 12/1946 Dunnebeck 91-395 3,054,385 9/1962 Hanna 91-395 PAUL E. MASLOUSKY, Primary Examiner 

